Introduction:
This experiment was designed to carry out to completion the acid catalyzed dehydration of cyclohexene from cyclohexanol. Within organic chemistry, elimination reactions fall under that broad category of transformations. There are two types of elimination reactions, E1 and E2. An E1 reaction was carried out in this experiment. The E1 reactions are most mechanistically similar to SN1 reactions, but also compete with both types of substitution reactions. E1 reactions occur in two steps. The first step requires the loss of the leaving group from the electrophile. However, if the leaving group attached to the electrophile happens to be an OH group it must be protonated by a strong acid. Protonation creates H20, a more acceptable leaving group compared to OH. With the absence of the leaving group, an intermediate carbocation is formed. The original protonation of the OH group also spurs the formation of a weak base, which is able to pluck a beta hydrogen from the electrophile. The end result is the formation of an alkene between the carbon the leaving group was attached to and the remaining hydrogen. It is also important to mention that elimination reactions only occur when heat is involved. Infrared spectroscopy will be preformed to allow certain characteristics of the molecule to be seen based on comparison of the frequencies of the bonds within the molecule and frequencies of the absorbed radiation.
cyclo.jpg
Cyclohexanol Cyclohexene Data:
The temperature graph begins at 0; but, the actual elapsed time to 0 was 58 minutes where the temperature held steady at 27 C. The 0 mark beginning of the graph indicates the time when the vapor made it to the top of the aparatus and the temperature began to rise.
Tempgraph.jpg
Infrared Spectroscopy
The top graph is the graph from our teams experiment. The slight dip under the title "terrycyclohexene" is an indication that H2O (H-O-H) is present in the sample. By comparing our graph with another teams graph, "tomcyclohexene" below, we see that the top sample had less H2O and was therefore more pure. It is also interesting to note the spike at approximately 2400 has grown, nearly doubling from the time of the first graph below "tomcyclohexene" to the time of the top graph "terrycyclohexene". According to Dr. Higginbotham, this spike represents CO2 (O=C=O) and was present in the sample due to the exhalation from just a few individuals in the room.
:
graph11.jpg
Analysis:
Theoretical yield: in the equation the phosphoric acid is acting as the catalyst.
fosforic.jpg
Theoretically 0.074 moles(7.411g) of cyclohexanol should produce 0.074 moles of cyclohexene, cyclohexene by multiplying the MW of cyclohexene (82.1 g/mol). 0.074 mol x 82.1 g/mol = 6.075 g of cyclohexene
In other words, 7.411g of cyclohexanol should produce 6.075 g of cyclohexene, known as the theoretical yield.
3.368 grams of Cyclohexene (experimental yield)x 100 = 55.44 % yield recovered 6.075 grams of Cyclohexene (theoretical yield)
Conclusion:
The success of distillation and the purity of the product was measured using infrared spectroscopy. In addition, the IR spectrum graph of the experimental product was then compared with a another spectroscopy done of a sample of cyclohexene.
The experimental IR spectrum graph above shows
cyclohexeneIR.jpg
a cyclohexene as one of the products. The elimination reaction E1 of an alcohol includes the loss of an OH from the carbon and the loss of an H from an adjacent beta carbon. Because the OH group is a very poor leaving group, an alcohol is able to undergo dehydration only if its OH group is converted into a better leaving group. One way to convert the OH group into a good Leaving group is to protonate it. In the first step of the dehydration reaction, protonation changes the very poor leaving group –OH into a good leaving group –OH2+.The resulting product is an alkene (pi-bond) and a molecule of water.
In most cases, an E1 reactions with an OH requires an acid catalyst and heat. In the experiment Phosphoric acid was used, one of the most common acid catalysts. When more than one elimination product can be formed, the major product is the more substituted alkene. This is achieved by removing a proton from the adjacent carbon that has fewer hydrogens, this is known as Zaitsev’s rule. The more substituted alkene is the major product because it is the more stable alkene, it has the more stable transition state leading to its formation.
The fact that the CO2 spike grew so much, in such a short time, and absorbs infrared energy so well, is a testament to the real threat it poses as it continues to increase in our atmosphere. *Here is a graph of a cyclohexene for comparison purposes (graph from http://orgchem.colorado.edu/)
Post Lab Question: Atom economy: the mass of the desired product divided by the mass of all reactants
Introduction:
This experiment was designed to carry out to completion the acid catalyzed dehydration of cyclohexene from cyclohexanol. Within organic chemistry, elimination reactions fall under that broad category of transformations. There are two types of elimination reactions, E1 and E2. An E1 reaction was carried out in this experiment. The E1 reactions are most mechanistically similar to SN1 reactions, but also compete with both types of substitution reactions. E1 reactions occur in two steps. The first step requires the loss of the leaving group from the electrophile. However, if the leaving group attached to the electrophile happens to be an OH group it must be protonated by a strong acid. Protonation creates H20, a more acceptable leaving group compared to OH. With the absence of the leaving group, an intermediate carbocation is formed. The original protonation of the OH group also spurs the formation of a weak base, which is able to pluck a beta hydrogen from the electrophile. The end result is the formation of an alkene between the carbon the leaving group was attached to and the remaining hydrogen. It is also important to mention that elimination reactions only occur when heat is involved. Infrared spectroscopy will be preformed to allow certain characteristics of the molecule to be seen based on comparison of the frequencies of the bonds within the molecule and frequencies of the absorbed radiation.
Data:
The temperature graph begins at 0; but, the actual elapsed time to 0 was 58 minutes where the temperature held steady at 27 C. The 0 mark beginning of the graph indicates the time when the vapor made it to the top of the aparatus and the temperature began to rise.
Infrared Spectroscopy
The top graph is the graph from our teams experiment. The slight dip under the title "terrycyclohexene" is an indication that H2O (H-O-H) is present in the sample. By comparing our graph with another teams graph, "tomcyclohexene" below, we see that the top sample had less H2O and was therefore more pure. It is also interesting to note the spike at approximately 2400 has grown, nearly doubling from the time of the first graph below "tomcyclohexene" to the time of the top graph "terrycyclohexene". According to Dr. Higginbotham, this spike represents CO2 (O=C=O) and was present in the sample due to the exhalation from just a few individuals in the room.
:
Analysis:
Theoretical yield: in the equation the phosphoric acid is acting as the catalyst.
Theoretically 0.074 moles(7.411g) of cyclohexanol should produce 0.074 moles of cyclohexene, cyclohexene by multiplying the MW of cyclohexene (82.1 g/mol).
0.074 mol x 82.1 g/mol = 6.075 g of cyclohexene
In other words, 7.411g of cyclohexanol should produce 6.075 g of cyclohexene, known as the theoretical yield.
3.368 grams of Cyclohexene (experimental yield) x 100 = 55.44 % yield recovered
6.075 grams of Cyclohexene (theoretical yield)
Conclusion:
The success of distillation and the purity of the product was measured using infrared spectroscopy. In addition, the IR spectrum graph of the experimental product was then compared with a another spectroscopy done of a sample of cyclohexene.
The experimental IR spectrum graph above shows
In most cases, an E1 reactions with an OH requires an acid catalyst and heat. In the experiment Phosphoric acid was used, one of the most common acid catalysts. When more than one elimination product can be formed, the major product is the more substituted alkene. This is achieved by removing a proton from the adjacent carbon that has fewer hydrogens, this is known as Zaitsev’s rule. The more substituted alkene is the major product because it is the more stable alkene, it has the more stable transition state leading to its formation.
The fact that the CO2 spike grew so much, in such a short time, and absorbs infrared energy so well, is a testament to the real threat it poses as it continues to increase in our atmosphere. *Here is a graph of a cyclohexene for comparison purposes (graph from http://orgchem.colorado.edu/)
Post Lab Question:
Atom economy: the mass of the desired product divided by the mass of all reactants
Cyclohexanol: Molecular Formula-C6H12O, Molecular Weight-100.58g/mol
Cyclohexene: Molecular Formula-C6H10, Molecular Weight-82.14g/mol and H20-18.053=100.193g/mol
Atom economy:
82.14/100.58 = 81.67%